Photoalignment technology allows the fabrication of spatially varying liquid crystal alignment patterns on photoalignment layers. One of the types of devices that may be fabricated utilizing photoalignment technology is a polarization grating (PG).
A PG is a sinusoidal phase grating made of a retardation film with spatially varying optical axis. Different from other optical gratings, a PG diffracts light into +1 and −1 diffraction order and all other higher orders are eliminated. Moreover, a PG has the highest diffraction efficiency among all diffraction gratings. Applications for PGs are devices based on diffraction optics. Conventionally, PGs are difficult to make due to the use of laser beam interference to create spatially varying alignment on the photoalignment layer, which has high sensitivity to small vibrations of equipment and to airflow.
There are different polarization converters and polarizers that convert input light with a specified polarization state to output light with another specified polarization state. The conversion efficiency is usually highly dependent on the polarization state of the input light, which means that if the input light is non-polarized, the conversion efficiency of conventional converters and polarizers will decrease significantly.